I'll offer my opinion - others' opinions may vary:
I have a Novation Impulse 49 that I used for several years.
The keyboard itself is VERY nice, IMHO ~
The keybed, pads, rotary & slide controls all feel and work great, and it has some VERY cool programmable arp and key-split functions.
However, the Automap control surface implementation with Sonar, for me at least, has always basically sucked.
Windows 7 and 8, Sonar X3 and Platinum, varying versions of Automap.
Unreliable, difficult to map, control dropouts for no apparent reason, etc., etc.
Manually mapping to VST controls without using Automap probably works fine.
I wound up using Azlow's great Sonar utility (search the forums here) and a custom setup for the Impulse 61 posted on his website. Worked pretty well for the most part, but for some reason it always remapped the MIDI channel on the Mod wheel, and I never dug deep enough into the utility to figure out why the channel was changing. Work arounds are easy enough to implement with some track settings in Sonar, but for me it was still a bit of a PITA to have to worry with all the time.
In no longer use my Impulse 49 as my primary controller for Sonar, but it's still a GREAT keyboard for controlling individual VST's and external modules. If you can get one in your price range and aren't too concerned about control surface implementation in Sonar (or don't mind the chance you'll need to tinker a lot to get the faders and knobs to map properly in 'mixer' mode), it will probably work fine for you.
FWIW...